THE CIRCULATION OP THE BLOOD. 



225 



their plasticity; the small size of some of the capillaries, barely 

 allowing the corpuscles to be squeezed through; the changes in 

 the velocity of the current, especially in the capillaries ; its pos- 

 sible arrest or retrocession ; the velocity in one so much greater 

 than in its neighbor, without very obvious cause — all this and 



Fig. 195.— Portion of the web of a frog's foot as seen under a low magnifying power, 

 showing the blood-vessels, and in one corner the pigment-spots (after Huxley), a, 

 small arteries (arterioles); v, small veins. The smaller vessels are the capillaries. 

 The course of the blood is indicated by arrows. 



much more forms, as we have said, a remarkable lesson for the 

 thinking student. This, like all microscopic views, especially 

 if motion is represented, has its fallacies. It is to be remem- 

 bered that the movements are all magnified, or else one is apt 

 to suppose the capillary circulation, extremely rapid, whereas 

 it is like that of the most sluggish part of a stream, and very 

 irregular. 



15 



